(5x³-x²+2x-3)(4x²-x+2)

=20x⁵-5x⁴+10x³-4x⁴+x³-2x²+8x³-2x²+4x-12x²+3x-6

=20x⁵-9x⁴+19x³-16x²+7x-6

(x-1)(x+1)(x+2)

=(x²-1)(x+2)

=x³+2x²-x-2

TONGXAU
const
fi='tongxau.inp';
fo='tongxau.out';
var
f:text;
a:array[1..32000] of char;
t,s,so,nul,i,n:integer;
procedure inp;
begin
assign(f,fi);
reset(F);
n:=0;
while not(eof(f)) do
begin
inc(n);
read(f,a[n]);
end;
close(F);
end;
procedure out;
begin
assign(f,fo);
rewrite(F);
i:=1 ;
s:=0;
while i<=n do
begin
t:=0;

while a[i] in ['0'..'9'] do
begin
val(a[i],so,nul);
t:=t*10+so;
inc(i);
end;
s:=s+t ;
inc(i);
end;
write(f,s);
close(f);
end;
BEGIN
INP;
OUT;
END.

6 x (236 - X) = 624

236 - x = 624 : 6 = 104

x = 236 - 104 = 132

b) X x a = aaa

X x a = 100a + 10a + a

X x a = 111a

Vậy x = 111

c) xx - x = 30

11 x X - X = 30

X x (11 - 1) = 30

X x 10 = 30 

X = 30 : 10 = 3

Vậy x = 3    

-\(\dfrac{1}{4}\)- -5+\(\dfrac{1}{3}\)-\(\dfrac{3}{2}\)-3-\(\dfrac{7}{4}\)+\(\dfrac{4}{3}\)

=-\(\dfrac{1}{4}\)+5+\(\dfrac{1}{3}\)-\(\dfrac{3}{2}\)-3-\(\dfrac{7}{4}\)+\(\dfrac{4}{3}\)

=-(\(\dfrac{1}{4}\)+\(\dfrac{7}{4}\))+(5-3)+(\(\dfrac{1}{3}\)+\(\dfrac{4}{3}\))-\(\dfrac{3}{2}\)

=-2+2+\(\dfrac{5}{3}\)-\(\dfrac{3}{2}\)

=\(\dfrac{1}{6}\)

219-7(x+1)=100

7(x+1)=219-100

7(x+1)=119

x+1=119:7

x+1=17

x=17-1

x=15=6 

(x+2)(x+1)-(x-3)(x+5)=0

\(\Leftrightarrow\) (x²+x+2x+2)-(x²+5x-3x-15)=0

\(\Leftrightarrow\)x²+x+2x+2-x²-5x+3x+15=0

\(\Leftrightarrow\)x+17=0

\(\Rightarrow\)x=-17